"Smart-Windows" such as described in U.S. Pat. No. 4,832,463 entitled "Thin Film Ion-Conducting Coating", primarily consist of thin coatings on a transparent substrate whereby the reflective and transmissive properties of the electrochromic coatings can be electrically controlled. This Patent is incorporated herein for reference purposes and should be reviewed for its description of durable, environmentally stable materials that meet many of the automotive, aircraft and military performance specifications.
A first use for such "smart-windows" is in existing buildings wherein the expense of replacing existing plate glass windows with "smart-windows" would be prohibitably expensive.
The aforementioned U.S. Patent suggests depositing the electrochromic device on a flexible plastic substrate, such as mylar, which is a trademark of DuPont Company for a flexible polyester film. The provision of the electrochromic coatings on the flexible mylar film would transform ordinary windows to so called "smart-windows", when the electrochromic mylar is attached to the interior or exterior surface of such windows.
However, when electrochromic materials are deposited by conventional vacuum deposition techniques such as thermal evaporation or RF sputtering, on to a transparent substrate for all but one of the materials the substrate must remain at an elevated temperature in order to control the electrical and optical properties of the device. Therefore, the use of conventional vacuum deposition techniques has heretofore not proved feasible for conventional plastic materials since the plastics deteriorate when subjected to high temperatures for the required periods of time.
Another impediment to the widespread commercialization of electrochromic smart windows is the occurrence of pinholes and other electronically-shorting pathways which result from ordinary low temperature depositions of the middle layer, since such deposition techniques lead to porous, low density layers.
An additional impediment to the widespread commercialization of electrochromic smart windows is that long deposition times are required to build-up the five coatings used to provide the electrochromic effect. With the method described in the aforementioned U.S. Patent, the two outer layers must exhibit a high degree of crystallinity whereas the middle layer must remain amorphous. The common substrate was accordingly heated during the deposition of the first two layers, cooled during the deposition of the third middle layer and thereafter heated during the deposition of the final forth and fifth layers. Whereas the long heating and cooling cycles are not conducive to commercial production, the substrate high temperature heating requirement eliminates most commercially available plastic materials.
A paper entitled "Modification of the Optical and Structural Properties of Dielectric ZrO.sub.2 Film by Ion-Assisted Depositions" which appeared in the Journal of Applied Physics, 55, January, 1984, describes the ion-assisted deposition of ZrO.sub.2 films on both heated and unheated substrates. The ZrO.sub.2 films were prepared by electron-beam evaporation of ZrO.sub.2 accompanied by irradiation with a 600-eV argon beam. When the argon beam was employed, the refractive index and mass density of the ZrO.sub.2 on the heated substrate, however, was higher than the refractive index and mass density of the ZrO.sub.2 on the unheated substrate.
One purpose of the instant invention, accordingly, is to provide a method for depositing high mass density electrochromic device materials upon transparent substrates by means of a rapid deposition process that does not require a heated substrate to achieve the desired electrochromic effects.